The cladogram depicting whale evolution is from the book Evolution: The Triumph of an Idea by Carl Zimmer. The artwork is a slight modification of the illustration by Carl Buell
in At the Water's Edge by Zimmer. The book is a companion to the PBS series of the Evolution Project, a coproduction of the WGNH/NOVA Science Unit and Clear Blue Sky Productions.
Please visit the extensive website for this production.

It was not until 1979 that paleontologists had their first indisputable evidence about whale transition. Pakicetus was discovered by Philip Gingerich in Pakistan. Later, in 1995,
Hans Thewissen found Ambulocetus. Whales with legs are now known from Pakistan, India, Egypt and the U.S.A.

It took less than 15 million years for the whale lineage to move from land, through shallow bays and coastal waters, to deep marine environments. By 40 million years ago whales had become
essentially the animals we know today.

The evolution of whales involved much more than legs becoming flippers or vestigial organs. The fossil series demonstrates how their breathing apparatus changed, their ears changed and
other body parts changed. If you are interested in detailed taxonomic descriptions, click on an animal illustrated at right to be taken to another website with that information.

Whales did not turn into fish. Inside every flipper is found the bones of the mammalian hand. They swim like otters by undulating the mammalian spine. The tail fluke is not a fish fin.
Evolution works by modifying existing body plans to fit new conditions of life, and is often constrained by developmental pathways. No longer limited by gravity and strength of bones,
whales could become giants of the sea.

To learn more about whale evolution and the many transitional forms, use the hotlinks in the text above or in the bibliography given below.

As Stephen Gould concludes, "If you had given me a blank piece of paper and a blank check, I could not have drawn you a theoretical intermediate
any better or more convincing than Ambulocetus. Those dogmatists who by verbal trickery can make white black, and black white, will never be convinced of anything, but Ambulocetus
is the very animal that they proclaimed impossible in theory."
Natural History magazine, May 1994.

Cetaceans have unique semicircular canals that allow them to be highly acrobatic swimmers without becoming dizzy.
By investigating this organ in ancient fossils, the researchers found that early whales acquired this special trait
quickly and early on in their evolution. This was a defining event that likely resulted in their total independence of life on land.

The research paper by Spoor F. et al., Vestibular Evidence for the Evolution of Aquatic Behaviour in early Cetaceans,
Nature 417:163-166 (2002), is available here.

Side view of the inner ears of, left to right, a land mammal (bushbaby), a land-living early whale from Pakistan (
50-million-year-old Ichthyolestes), a marine early whale from India (45-million-year-old Indocetus), and a modern dolphin.
The latter two aquatic species have much smaller semicircular canals than the former two. Image reconstructed from computed
tomography scans, adjusting for body size differences between the animals. Each inner ear would easily fit on a penny.
[Image by F. Spoor]

PBS on Whale Evolution :
A 7-minute video describes two lines of evidence, fossil and molecular, which contribute to our
picture of evolution. It focuses on whales, which provide an excellent opportunity to examine the transition between
species because so many intermediate fossils have been found.

Cetacean Evolution : This site also provides you with complete background
information on every living species of whale, dolphin and porpoise known. Cetacea.org is currently on hiatus.
Estimated re-launch Spring-Summer 2007..

Tinker, Spencer Wilkie, 1988, Whales of the World. J. Brill:310 pages. [Hard to find, but the only guide to modern cetacea which describes the osteology]

Up-to-date information can be found in the Handbook of Marine Mammals, edited by S. H. Ridgeway and J. H. Harrison, published by Academic Press in 1981 and later. These are
horrendously expensive little volumes, but are the best source of data on all the marine mammals